Such cell for SOFC has a structure wherein a unit cell is formed by bonding an air electrode to one face of an electrolyte layer and bonding a fuel electrode to the other face of this electrolyte layer, and this unit cell is clamped between a pair of electron-conductive alloys or the like which give/receive electrons to/from the air electrode or the fuel electrode.
And, such SOFC cell is operable at an operating temperature e.g. from 700 to 900° C. approximately, so that in association with ion migration from the air electrode to the fuel electrode via the electrolyte layer, an electromotive force is generated between the pair of electrodes and this electromotive force can be taken out of the cell for its utilization.
The alloy employed in such SOFC cell is made from a Cr-containing material having good electron conductivity and oxidation resistance. And, such heat resistance of the alloy is attributable to a dense coating layer of chromia (Cr2O3) formed on the surface of this alloy.
Further, with the SOFC cell, during its manufacturing process, for such purpose as minimizing the contact resistance between the alloy and the air electrode or the fuel electrode, there is sometimes conducted a sintering treatment effected at a sintering temperature ranging from 1000 to 1250° C. approximately, which is higher than the operating temperature (see. e.g. Patent Document 1).
On the other hand, there is also a technique attempting to restrict oxidation of Cr contained in the alloy into a hexavalent oxide which can easily scatter about, by subjecting the surface of the alloy employed in SOFC cell to a coating layer forming treatment which forms on the alloy surface an n-type semiconductor coating layer obtained by doping a mono metal oxide) with an impurity (see, e.g. Patent Document 2).